Gas expanded latex



Oct. 8, 1940. V ROBERTS I 2,216,785

GAS EXPANDED LATEX Filed Oct. 31. 1936 LATEX AQUEOUS RUBBER EMULSION LATEX PouREn POROUS MOULD LATEX GASSED umvnNe OFF WATER THROUGH POROUS MOLILD XPANDED LATEX VULCANlZED AT ROOM TEMPERATURE INVENTOR. flM/wl leaf $3 fioberfs .diwzw ATTORNEY.

Patented on. s, 1940 UNITED STATES PATENT OFFICE GAS EXPANDED LATEX Dudley D. Roberts, New York, N. Y., assignor to Rubatex Products, Inc., New York, N. Y., a corporation of Delaware Application October 31, 1936, Serial No. 108,643

Claims.

masticated and milled to form a rubber dough and mixed with suitable ingredients for expanding, and vulcanizing the dough. The United States Patent No. 1,905,269 to G. P. Denton and the application Serial No. 717,550, filed March 27, 1934, describe successful commercial processes for manufacturing gas expanded rubber. These processes essentially comprise the'steps of gassing the dough in an autoclave while subjecting it to a temperature for partially vulcanizing the dough and then finally vulcanizing and expanding the gassed dough in suitable molds. Complicated molds could not be used and accurate cutting and trimming of the gassed dough before insertion into the molds was required to insure proper expansion in the mold.

In accordance with our present invention, we contemplate manufacturing gas-expanded rubber using liquid latex as the rubber base mixed with suitable ingredients to form a gelatinous or liquid mixture for carrying out the process. A

porous mold is used so that upon the high pressure gassing of the mixture, the water is forced through the mold which retains the compound in a semi-dry or dry state. We employ a vulcanizer which is effective at room temperatures and effects the vulcanization of the final product without application of heat.

By employing a liquid rubber mixture, we are enabled to use molds of the most complicated shape and form since the liquid reaches remote crevices of the mold and the expansion of the mixture accurately fills the mold. Since the curing of the gassed latex can be efiected without application of heat, a simple plaster may be used for the mold since curing does not exert excessive pressures against the mold falls due to heating of the confined gas cells as in the conventional processes. A porcelain mold is equally suitable;

We have found that the latex mixture has a greater gas perviousness than the rubber dough compositions used in the prior art. Accordingly, the time required for gassing in the high pressure gassing chamber is diminished, making for greater economy in production by having a higher use factor of the expensive gassing equipment. The gassed latex has also been found to retain the gas upon removal from the autoclave even though Jno heat is applied thereto to partially cure it as the prior art requires. Due to the gas pervious character of the latex mixture, the homogeneous gassing is readily accomplished. Since no heating of the gassed dough is required, an important advantage is had over prior processes due to the 5 extreme difiiculty of uniformly internally heating a mass of rubber which is itself a good thermal insulator.

In a modified form of our process, the gassed latex is removed from the autoclave in a semi-dry condition and is subsequently dried and finally cured and expanded in a heated atmosphere to still further shorten the time necessary to retain each charge in the chamber.

In still a further modification of our present invention, the liquid latex mixture is gassed and semi-dried in the autoclave and also semi-cured therein, and then removed. The semi-cured gassed latex is then finally cured in a mold or in hot air.

Our process of manufacturi as-expanded rubber is less expensive than conventional processes due to the shorter gassing cycle required wherein a greater utilization of the autoclave equipment is had, and also due to the cheaper molds and final curing stage required, since the final curing does not require expensive steam platens or electric ovens using pressure resisting molds, but rather is curable at a relatively low temperature and low internal pressure.

It is accordingly an object of our invention to provide a novel process for manufacturing gasexpanded rubber material using a liquid latex base.v

It is another object of our invention to provide a novel process for manufacturing gas-expanded rubber products using a liquid or gelatinous mixture expandible in very complicated forms.

It is a further object of our present invention to simplify and reduce the production costs in the manufacture of gas-expanded rubber materials.

It is still a further object of our invention to provide a novel process in the manufacture of gas-expanded rubber products whereinthe final curing of the rubber is carried out at room temperature or at relatively moderately heated conditions;

These and further objects of our present invention will become apparent in the following description and in the appended claims.

In carrying out our process, we employ a liquid latex concentrated as it comes from the tree having a composition of approximately 60% rubber and 40% water. The composition of the mixture which we have found yields very satisfactory results contains approximately the following proportions by weight:

The physical appearance of-this mixture is that of a milw white liquid. Other ingredients and proportions are feasible. Latex either more concentrated or more-dilute than here specified maybe used. I

Darvan is a dispersing agent for latex. It is a synthetic organic chemical. Physically it is a rubber. It is manufactured by Dewey and Almy of Cambridge, Massachusetts.

' In one modification, the latex mixture is poured into a porous mold or on a porous plate. A plaster or porcelain material may be used to provide the porosity required for confining the mixture in the gassing chamber. The gassing of the latex mixture is carried out in a gassing chamber or autoclave'preferably at a pressure of the order of 3000 pounds of nitrogen gas. Difierent, inert gases and gas pressures maybe used as"prac-- and is readily homogeneously gassed in the eham- I ber. Thorough gassing is accomplished, in most instances, in about one and one-half hours. No heating is necessary at thisstage to produce a semi-dry, thoroughly gassed dough. When the gas pressure is rele ed,., the latex is found to be coagulated and expanded to approximately The gassed latex.

four times its initial volume. expands after the water has been partially removed and the pressure is released. The gassed latex may then be removed from the porous mold and is permitted to dry. It-vulcanizes at room temperature due to the powerful accelerator, butyl z ymate, employed. Butyl zymate vulcanizes the latex at room temperature without application of heat. when the product is finally dry, the process is completed. The product may be made soft or medium hard by using the composition hereinbefore stated. To produce hardened expanded latex, it is necessary to add a further ingredient, for example liquid Bakelite, to the latex mixture.

In a modified form of our process, the gassing period of the latex mixture is relatively shortened and the semi-dry gassed dough is quickly removed from the autoclave to a heated chamber or room containing hot air where the final curing of the product is carried on. The temperature of the hotroom is less than the temperatures employed in the heated platens or ovens used in prior processes; it is a temperature rather for drying the material, since the vulcanization can ,be effected at room .temperatures as already stated. By reducing the gassing period, a, greater amount of latex can be gassed in a given time,

making for more economical utilization of the gassing equipment for reducing production costs of the expanded latex products.

A further modification of my process is somewhat similar to the process described in the Benton patent referred to hereinabove in that the charge is semi-cured whiieitis in the autoclave. In accordance with this modification, the

, latex mixture is poured in a mold or a porous plate and subjected to a pressure of theorder of 8000 pounds per square inch in an autoclave.

- The water is forced outthrough the porous walls of'the mold and a semi-dry mixture is produced. When the latex is semi-dry, the autoclave is heatedby steam pressure in a manner well known in the art to a semi-curlng.temperature while maintaining the gaseous pressure in the autoclave. It is accordingly noted that this modification differs from the Dentonprocess in that it is necessary to force the water out of the mixture during the gassing thereof before the mixture is subsequently partially vulcanized. The remainder of this process comprises in cooling the chamber and then finally releasing the gas pressure and removing the coagulated charge from the chamber. The gassed latex is then finally vulcanized and dried in a mold at suitable temperature or in hot air. 7

Our process may be carried out with various other modifications than those described. 'It is to be understoodthat the latex used as the base of the mixture maybe inconcentrated or dilute form and may be mixed in varying percentages with sulphur, fillers and'accelerators and other compounding ingredients-known in the art. 'lhe mixture may be gassed. at any stage in the process, for examplebefore forming in molds.

quent to the gassing thereof. A porous mold is used when the mixture is'dried by the action of the gaseous pressure which forces the moisture through the porous walls. However, by subsequent drying, which may be aided by heating, standard non porous molds may be used for the gassing and coagulated stages.

The gassing of the latex mixture need not be carried out in the molds tov which it is to be finally formed but may be carried out in any container and subsequently molded and dried. The latex mixture may be gassed in a liquid state, causing gas bubbles to form throughout the mixture. By using a suitable jelling agent such as sodium silico fiuoride in the latex mixture, it is caused to set, confining the gas bubbles therein. Ajelled mass containing a multitude of gas bubbles results, which may be molded and dried to form the gas expanded latex product.

a A liquid latex mixture containing a jelling agent may be gassed in non-porous molds to cause the formation of a myriad of minute gaseous bubbles which areheld therein by .the jelling of the mass. The gassed mixture swells'to fill the mold and may be removed therefrom after setting. The jelled, molded mass is then dried to complete the process. I 1

The dmwing shows diagrammatically the process described above.

, Although particular compositions and condi-- rubber products which comprises placing rubber in liquid form in a porous structure, subjecting the rubber to a neutral gas at a pressure of the order of 3000 pounds per square inch to force the water in the rubber through said porous structure to dry and gas impregnate the rubber, releasing the gaseous pressure to permit expansion of the rubber to fill the structure, and finally drying and curing the gas expanded rubber.

2. The method of manufacturing gas expanded rubber product's which comprises placing rubber in liquid form in a porous mold, subjecting the rubber to a neutral gas at high pressure to force the water in the rubber through said porous mold to partially dry and gas impregnate the rubber, releasing the gaseous pressure to permit expansion of the rubber to fill the mold, and heating the rubber for final drying and vulcanization thereof.

3. The method of manufacturing gas expanded gas retaining latex products which comprises placing latex in aqueous form in a porous mold, subjecting the latex to a neutral gas at high pressure to force the water in the latex through said porous mold to partially dry and gas impregnate the latex, then heating the latex to partially vulcanize it, releasing the gaseous pressure to permit expansion of the latex to fill the mold, and heating the latex for final drying and vulcanization thereof. l

4. The method of producing gas expanded latex products which comprises'forming an aqueous latex mixture; placing the aqueous latex mixture in a porous mold; subjecting the aqueous latex mixture to a neutral gas at a relatively high pressure to drive off the water and to gas impregnate the latex; expanding the gas, impregnated latex and vulcanizing the gas expanded latex structure to a permanent cure.

5. The method of manufacturing gas expanded gas retaining latex products which comprises placing latex in aqueous form in a porous mold, subjecting the latex to a neutral gas at high pressure to force the water in the latex through said porous mold to partially dry and gas impregnate the latex, releasing the gaseous pressure to permit expansion of the latex, and vulcanizing the gas expanded gas retaining latex.

DUDLEY D. ROBERTS. 

